Method and an apparatus for encoding or decoding a video signal

ABSTRACT

A method of processing a video signal is disclosed. The present invention includes receiving prediction information of a macroblock and filer information, predicting a current picture using the prediction information of the macroblock, and applying a filter using the predicted current picture and the filter information. 
     Accordingly, accuracy of prediction can be enhanced by applying a filter to a frame predicted before a residual for a predicted frame is coded. As the residual is reduced, efficiency of video signal processing can be enhanced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application61/040,123, filed Mar. 27, 2008, U.S. Provisional Application61/048,226, filed Apr. 28, 2008, U.S. Provisional Application61/073,008, filed Jun. 16, 2008 and U.S. Provisional Application61/076,691, filed Jun. 30, 2008, and claims the benefit of South KoreaApp. No. 10-2009-0025691, filed Mar. 26, 2009, all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an apparatus for encoding or decoding avideo signal and method thereof.

BACKGROUND ART

In transmitting an encoded video signal to a decoder, a method ofremoving temporal redundancy and spatial redundancy to raise acompression ration of a video signal, i.e., an intra prediction methodand an inter prediction method are used.

DISCLOSURE OF THE INVENTION Technical Problem

An object of the present invention is to improve efficiency of coding incoding a residual for a current frame.

Another object of the present invention is to enhance accuracy of interprediction.

Another object of the present invention is to enhance efficiency ofcoding in coding filter information.

Technical Solution

The present invention is characterized in applying a filter forminimizing a difference between a predicted frame by performing intra orinter prediction and an original frame.

The present invention is characterized in applying a filter prior tostoring a reconstructed frame in a decoded picture storing unit, storinga frame through the filter in the decoded picture storing unit, andusing the stored frame for inter prediction.

The present invention is characterized in compensating for anillumination intensity difference between an original frame and areconstructed frame.

The present invention is characterized in using a flag indicatingwhether to apply filter information of a previous frame to a currentframe in obtaining a filter to apply to the current frame.

The present invention is characterized in using a difference filterbetween a filter of a current frame and a filter of a previous frame inobtaining a filter to apply to the current frame.

The present invention is characterized in using a prediction filter anda difference filter between a filter of a current frame and theprediction filter in obtaining a filter to apply to the current frame.

The present invention is characterized in updating a prediction filterapplied to a current frame into a filter applied to a previous frame.

Advantageous Effects

Accordingly, the present invention provides the following effects oradvantages.

First of all, the present invention is able to improve accuracy ofcurrent frame prediction by applying a filter to a frame predictedbefore coding a residual for a current frame and is able to enhanceefficiency of video signal processing by reducing the residualcorrespondingly.

Secondly, a difference between an original frame and a reconstructedframe can be reduced by applying a filter in a reconstructed frame,whereby accuracy of reconstruction can be improved. And accuracy ofinter prediction can be improved by using a reconstructed frame as areference frame.

Thirdly, by compensating for an illumination intensity for areconstructed frame, error attributed to various rounding operations ina video signal processing process can be reduced. And, accuracy can beimproved in reconstructing a frame.

Fourthly, it is able to efficiently code filter information of a currentframe using a flag indicating whether to apply filter information of aprevious frame to the current frame.

Fifthly, it is able to efficiently code filter information of a currentframe using a difference filter between a filter of the current frameand a filter of a previous frame.

Sixthly, it is able to efficiently code filter information of a currentframe using a prediction filter for a whole sequence.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a schematic block diagram of a video signal encoding apparatus(100) according to a first embodiment of the present invention;

FIG. 2 is a schematic block diagram of a video signal decoding apparatus(200) according to a first embodiment of the present invention;

FIG. 3 is a flowchart of a process for applying a filter to a currentframe predicted in an encoder according to a first embodiment of thepresent invention;

FIG. 4 is a flowchart of a process for applying a filter to a currentframe predicted in a decoder according to a first embodiment of thepresent invention;

FIG. 5 is a schematic diagram for a method of generating a filteraccording to the present invention;

FIG. 6 is a schematic block diagram of a video signal encoding apparatus(300) according to a second embodiment of the present invention;

FIG. 7 is a schematic block diagram of a video signal decoding apparatus(400) according to a second embodiment of the present invention;

FIG. 8 is a flowchart of a process for applying a filter to a currentframe through a deblocking filtering unit in an encoder according to asecond embodiment of the present invention;

FIG. 9 is a flowchart of a process for applying a filter to a currentframe through a deblocking filtering unit in a decoder according to asecond embodiment of the present invention;

FIG. 10 is a schematic diagram for a method of generating a filteraccording to the present invention;

FIG. 11 is a flowchart for a method of compensating for an illuminationintensity difference between an original frame and a reconstructed frameaccording to a third embodiment of the present invention;

FIG. 12 is a diagram for a method of coding a filter coefficient usingflag information according to a fourth embodiment of the presentinvention;

FIG. 13 is a diagram for a method of coding filter information using adifference filter according to a fourth embodiment of the presentinvention; and

FIG. 14 is a diagram for a method of coding filter information using aprediction filter according to a fourth embodiment of the presentinvention.

BEST MODE

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofprocessing a video signal according to the present invention includesreceiving prediction information of a macroblock and filer information,predicting a current picture using the prediction information of themacroblock, and applying a filter using the predicted current pictureand the filter information.

According to the present invention, in generating a prediction value ofthe macroblock, the prediction value of a current block with themacroblock is generated using the prediction value of a neighbor blockwith the macroblock in case of intra prediction.

According to the present invention, in the applying the filer, the fileris applied by considering a type of the macroblock, a quantizationparameter of the macroblock, a coded block pattern (CBP) of themacroblock and a block boundary strength between blocks.

According to the present invention, the applying the filer furtherincludes searching for a boundary area within a picture and the filteris applied by discriminating the boundary area and a non-boundary area.And the filer is applied in each region by dividing a frame by N*N size(where the N is a natural number).

To further achieve these and other advantages and in accordance with thepurpose of the present invention, an apparatus for processing a videosignal according to the present invention includes a receiving unitreceiving prediction information of a macroblock and filer information,a predicting unit predicting a current picture using the predictioninformation of the macroblock, and a filtering unit applying a filterusing the predicted current picture and the filter information.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of processing a video signalaccording to the present invention includes applying a deblocking filterto a decoded picture, applying a filter to the deblocking-filtereddecoded picture, and storing the filtered decoded picture in a decodedpicture buffer.

According to the present invention, in the applying the filter to thedeblocking-filtered decoded picture, the filer is applied by consideringa type of a macroblock, a quantization parameter of a macroblock, acoded block pattern (CBP) of a macroblock and a block boundary strengthbetween blocks.

According to the present invention, the applying the filter to thedeblocking-filtered decoded picture further includes searching for aboundary area within a picture and the filter is applied bydiscriminating the boundary area and a non-boundary area.

According to the present invention, the method further includescompensating for an illumination intensity difference between anoriginal picture and the filtered decoded picture for the filtereddecoded picture.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, an apparatus for processing a videosignal according to the present invention includes a deblockingfiltering unit applying a deblocking filter to a decoded picture, afiltering unit applying a filter to the deblocking-filtered decodedpicture, and a decoded picture storing unit storing the filtered decodedpicture in a decoded picture buffer.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, In obtaining filter information toapply to a current frame, a method of processing a video signalaccording to the present invention includes using a flag indicatingwhether to apply filter information of a previous frame to the currentframe.

According to the present invention, if the flag instructs to apply thefilter information of the previous frame to the current frame, thefilter information of the previous frame is used as a filter of thecurrent frame. If the flag instructs not to apply the filter informationof the previous frame to the current frame, the filter information ofthe current frame is used as the filter of the current frame

According to the present invention, the filter information of thecurrent frame is obtained from a difference value between the filterinformation of the previous frame and the filter information of thecurrent frame and the filter information of the previous frame.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of processing a video signalaccording to the present invention includes obtaining filter informationof a current frame from a difference filter between prediction filterinformation of the current frame and filter information of the currentframe and the predicted filter information.

According to the present invention, the prediction filter information ofthe current frame includes an average value of the filter information oneach frame of a whole sequence.

According to the present invention, the prediction filter information ofthe current frame uses a filter of a previous frame as a predictionfilter of the current frame.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. First of all, terminologies in the present invention can beconstrued as the following references. And, terminologies not disclosedin this specification can be construed as the following meanings andconcepts matching the technical idea of the present invention.Therefore, the configuration implemented in the embodiment and drawingsof this disclosure is just one most preferred embodiment of the presentinvention and fails to represent all technical ideas of the presentinvention. Thus, it is understood that various modifications/variationsand equivalents can exist to replace them at the timing point of filingthis application.

In the present invention, filter application is provided to enhanceefficiency of video signal processing. And, it is understood that theapplication of filter can be omitted if efficiency of video signalprocessing is lowered due to the filter application. Therefore, filterinformation is understood as including information indicating whether touse a filter as well as a filter coefficient, a filter size and thelike. In case of applying a filter, the present invention is not limitedby a specific method. Therefore, it is understood that a most efficientone is selected from various methods proposed by the present invention.

FIG. 1 is a schematic block diagram of a video signal encoding apparatus(100) according to a first embodiment of the present invention.

Referring to FIG. 1, a transforming unit (110), a quantizing unit (115),a coding control unit (120), an inverse-quantizing unit (130), aninverse-transforming unit (135), a deblocking filtering unit (140), afiltering unit (145), a decoded picture storing unit (150), a motionestimating unit (155), an inter predicting unit (160), an intrapredicting unit (170) and an entropy coding unit (180).

The transforming unit (110) obtains a transform coefficient value bytransforming a pixel value. For this case, a discrete cosine transformor wavelet transform is available. The quantizing unit (115) quantizesthe transform coefficient value outputted from the transforming unit(110). The coding control unit (120) controls whether to perform intracoding or inter coding on a specific block or frame. Theinverse-quantizing unit (130) inverse-quantizes the transformcoefficient value. The inverse-transforming unit (135) reconstructs theinverse-quantized transform coefficient value into an original pixelvalue. The deblocking filtering unit (140) is applied to each codedmacroblock to reduce a block distortion phenomenon. A picture throughthe deblocking filtering is stored in the decoded picture storing unit(150) to be used as a reference picture. The motion estimating unit 155searches reference picture for a reference block most similar to acurrent block using the reference pictures stored in the decoded picturestoring unit (150) and then delivers position information of thesearched reference block and the like to the entropy coding unit (180).The inter predicting unit (160) performs prediction of a current pictureusing the reference picture and then delivers inter coding informationto the entropy coding unit (180). The intra predicting unit (170)performs intra prediction with a decoded pixel within the currentpicture and then delivers intra coding information to the entropy codingunit (180). The filtering unit (145) is applied to a predicted currentpicture to reduce a difference between the predicted current picture andan original picture. The entropy coding unit (180) generates a videosignal stream by performing entropy coding on the quantized transformcoefficient, the inter coding information, the intra coding information,reference block information inputted from the motion estimating unit(160) and the like.

FIG. 2 is a schematic block diagram of a video signal decoding apparatus(200) according to a first embodiment of the present invention.

Referring to FIG. 2, a video signal decoding apparatus according to thepresent invention includes an entropy decoding unit (210), aninverse-quantizing unit (220), an inverse-transforming unit (225), adeblocking filtering unit (230), a filtering unit (235), a decodedpicture storing unit (240), an inter predicting unit (250) and an intrapredicting unit (260).

The entropy decoding unit (210) extracts a transform coefficient of eachmacroblock, a motion vector and the like by entropy-decoding a videosignal bitstream. The inverse-quantizing unit (220) inverse-quantizesthe entropy-decoded transform coefficient and the inverse-transformingunit (225) reconstructs an original pixel value using theinverse-quantized transform coefficient. The deblocking filtering unit(230) is applied to each coded macroblock to reduce a block distortionphenomenon. A picture through filtering is outputted or stored in thedecoded picture storing unit (240) to be used as a reference picture.The inter predicting unit (250) predicts a current picture using thereference picture stored in the decoded picture storing unit (240) andinter prediction information (e.g., reference picture index information,motion vector information, etc.) delivered from the entropy decodingunit (210). The intra predicting unit (260) performs intra predictionfrom a decoded pixel within a current picture. The filtering unit (235)is applied to the predicted current picture from the inter predictingunit or the intra predicting unit. The predicted current picture throughthe filtering unit (235) and a residual from the inverse-transformingunit are added together to reconstruct an original picture. In thefollowing description, a filtering process of the present invention isexplained in detail.

FIG. 3 is a flowchart of a process for applying a filter to a currentframe predicted in an encoder according to a first embodiment of thepresent invention.

First of all, an encoder predicts a current picture using intraprediction or inter prediction [S110]. Yet, in case of a macroblockusing intra prediction, intra prediction is performed using a predictedpixel neighbor to a current block within the macroblock instead ofperforming intra prediction using an already reconstructed pixel. Thefiltering unit (145) compares the predicted current picture to theoriginal picture and is then able to generate a filter that minimizes adifference between the compared pictures [S120]. A method of generatingthe filter will be explained with reference to FIG. 5 later.

Although accuracy for prediction of a current picture can be enhanced byapplying the generated filter to the predicted current picture, theapplication of the filter may reduce efficiency of video signalprocessing [S130]. If the filter application is efficient, the generatedfilter coefficient will be transferred to a decoder [S135]. If thefilter application is inefficient, information indicating that thefilter is not applied to the predicted frame will be transferred using aflag [S140].

FIG. 4 is a flowchart of a process for applying a filter to a currentframe predicted in a decoder according to a first embodiment of thepresent invention.

First of all, a decoder receives prediction information on a currentframe, a residual and filer information from an encoder [S145]. Like theencoder, a current frame is predicted through inter prediction or intraprediction using the prediction information of the current frame [S150].It is able to apply a filter transferred from the encoder to thepredicted current frame. An original frame is reconstructed by adding aresidual from an inverse-transforming unit to the predicted framethrough the filtering unit [S160].

FIG. 5 is a schematic diagram for a method of generating a filteraccording to the present invention.

Referring to FIG. 5, w[n] indicates a predicted pixel value of a currentpicture and is a value inputted to a filter. And, x[n] is a predictedpixel value of a filtered current picture. In case that a filter oforder N and with coefficients a_(i) is used, x[n] can be represented asFormula 1.

$\begin{matrix}{{x\lbrack n\rbrack} = {\sum\limits_{i = 0}^{N}{a_{i}{w\left\lbrack {n - i} \right\rbrack}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Moreover, s[n] is a pixel value of an original picture. If a differencebetween x[n] and s[n] is set to e[n], it is able to obtain a_(i) whichminimizes the e[n] and a_(i) can be represented as Formula 2.

a _(i)=arg min E{e ² [n]}  [Formula 2]

The E{e²[n]} can be represented as Formula 3.

$\begin{matrix}\begin{matrix}{{E\left\{ {e^{2}\lbrack n\rbrack} \right\}} = {E\left\{ \left( {{x\lbrack n\rbrack} - {s\lbrack n\rbrack}} \right)^{2} \right\}}} \\{= {{E\left\{ {x^{2}\lbrack n\rbrack} \right\}} + {E\left\{ {s^{2}\lbrack n\rbrack} \right\}} - {2E\left\{ {{x\lbrack n\rbrack}{s\lbrack n\rbrack}} \right\}}}} \\{= {{E\left\{ \left( {\sum\limits_{i = 0}^{N}{a_{i}{w\left\lbrack {n - i} \right\rbrack}}} \right)^{2} \right\}} + {E\left\{ {s^{2}\lbrack n\rbrack} \right\}} -}} \\{{2E\left\{ {\sum\limits_{i = 0}^{N}{a_{i}{w\left\lbrack {n - i} \right\rbrack}{s\lbrack n\rbrack}}} \right\}}}\end{matrix} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack\end{matrix}$

If it is differentiated to find the a_(i) which minimizes the expressionabove, Formula 4 is obtained.

$\begin{matrix}{{\frac{\partial}{\partial a_{i}}\begin{matrix}{{E\left\{ {e^{2}\lbrack n\rbrack} \right\}} = {{2E\left\{ {\left( {\sum\limits_{j = 0}^{N}{a_{j}{w\left\lbrack {n - j} \right\rbrack}}} \right){w\left\lbrack {n - i} \right\rbrack}} \right\}} -}} \\{{2E\left\{ {{s\lbrack n\rbrack}{w\left\lbrack {n - i} \right\rbrack}} \right\}}} \\{= {{2{\sum\limits_{j = 0}^{N}{E\left\{ {{w\left\lbrack {n - j} \right\rbrack}{w\left\lbrack {n - i} \right\rbrack}} \right\} a_{j}}}} -}} \\{= {2E\left\{ {{w\left\lbrack {n - i} \right\rbrack}{s\lbrack n\rbrack}} \right\}}}\end{matrix}}{{i = 0},\ldots \mspace{14mu},N}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

If w[n] and s[n] are stationary, R_(w)[m] and R_(ws)[m] knownrespectively as the autocorrelation of w[n] and the cross-correlationbetween w[n] and s[n] are defined as Formula 5.

R _(w) [m]=E{w[n]w[n+m]}

R _(ws) [m]=E{w[n]s[n+m]}  [Formula 5]

The Formula 4 can be represented as Formula 6 by using the Formula 5.

$\begin{matrix}{{{\frac{\partial}{\partial a_{i}}E\left\{ {e^{2}\lbrack n\rbrack} \right\}} = {{2{\sum\limits_{j = 0}^{N}{{R_{w}\left\lbrack {j - i} \right\rbrack}a_{j}}}} - {2{R_{sw}\lbrack i\rbrack}}}}{{i = 0},\ldots \mspace{14mu},N}} & \left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

The a_(i) is obtained by letting the derivative be equal to zero.

$\begin{matrix}{{\begin{bmatrix}{R_{w}\lbrack 0\rbrack} & {R_{w}\lbrack 1\rbrack} & \ldots & {R_{w}\lbrack N\rbrack} \\{R_{w}\lbrack 1\rbrack} & {R_{w}\lbrack 0\rbrack} & \ldots & {R_{w}\left\lbrack {N - 1} \right\rbrack} \\\vdots & \vdots & \ddots & \vdots \\{R_{w}\lbrack N\rbrack} & {R_{w}\left\lbrack {N - 1} \right\rbrack} & \ldots & {R_{w}\lbrack 0\rbrack}\end{bmatrix}\begin{bmatrix}a_{0} \\a_{1} \\\vdots \\a_{N}\end{bmatrix}} = \begin{bmatrix}{R_{sw}\lbrack 0\rbrack} \\{R_{sw}\lbrack 1\rbrack} \\\vdots \\{R_{sw}\lbrack N\rbrack}\end{bmatrix}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The a_(i) can be obtained from the Formula 7.

A process of applying a filter by considering a type of macroblockaccording to a first embodiment of the present invention is explained.

First of all, an encoder is able to generate a macroblock map, on whicha type of a macroblock, i.e., an intra-macroblock or an inter-macroblockis marked. It is able to categorize a frame into a category including anintra-macroblock or an inter-macroblock only using the macroblock map.Filter information suitable per category is generated. The filterinformation is then transferred to a decoder.

The decoder receives a type of a macroblock from the encoder, andgenerates a macroblock map by using the type of a macroblock. Or A thedecoder receives information of a macroblock map from the encoder, andgenerates a macroblock map by using the information of a macroblock map.A category is sorted per type of macroblock using the generatedmacroblock map. Filtering is performed on a predicted frame by applyingthe filter information transferred from the encoder to each category.

A process of applying a filter by considering a quantization parameteraccording to a first embodiment of the present invention is explained.

First of all, a quantization parameter may differ per macroblock. If thequantization parameter is large, a range of quantized values is smalland a compression ratio is high. But, the quantized values have bigdifferences from an original signal. On the contrary, if a quantizationparameter is small, quantized values become proximate to an originalsignal but a compression ratio is lowered. Hence, the quantizationparameter affects an image quality of a reconstructed picture.

A category is sorted per quantization parameter of a macroblock. Filterinformation suitable for each macroblock can be generated with referenceto the category. The generated filter information is transferred to adecoder. It is then able to perform filtering per quantization parameterusing the generated filter information.

A process of applying a filter by considering a coded block pattern(CBP) according to a first embodiment of the present invention isexplained.

First of all, a coded block pattern (CBP) is a value indicating whetherdata exists within a macroblock. For instance, if a coded residual exitswithin a macroblock, reconstruction will be performed by adding theresidual to a predicted macroblock. If a coded residual fails to exitwithin a macroblock, reconstruction will be performed by a predictedmacroblock itself. Hence, a characteristic of an image may varyaccording to the CBP.

By considering the CBP, it is able to categorize a frame. It is able togenerate a filter suitable per category. The filter information istransferred to a decoder. It is able to perform filtering per CBP usingthe filter information.

A process of applying a filter by considering a boundary strengthaccording to a first embodiment of the present invention is explained.

First of all, a deblocking filter is provided to reduce a blockdistortion phenomenon and can be used by changing a strength of filter.But, a filter can not be used if efficiency of video signal processingis lowered due to the filter application. This depends on a boundarystrength and a variation of an image sample around a boundary. And, theboundary strength is determined according to a relation with a presenceor non-presence of an intra-coded macroblock, a motion vector value, areference block or the like. Hence, the boundary strength es related toa characteristic of image.

Based on a boundary strength, it is able to categorize a frame through adeblocking filter. It is able to generate a filter suitable for eachcategory. The filter information is transferred to a decoder. And, it isable to perform filtering per boundary strength using the filterinformation. Yet, in case that a filter is applied per category based onthe boundary strength, deblocking filtering is omitted.

A process of applying a filter by considering a boundary area accordingto a first embodiment of the present invention is explained.

First of all, it is able to apply a filter to each area by categorizinga frame into a boundary area and a non-boundary area. A filtering unitreceives a current frame predicted via inter or intra prediction. Byperforming a boundary search on the current frame through the deblockingfilter based on threshold values for determining a presence ornon-presence of a boundary, it is able to obtain a boundary area and anon-boundary area. Filter information to be applied to the boundary areaor the non-boundary area is generated. The generated filter information,the threshold values and the like are transferred to a decoder. Thedecoder sorts a boundary area and a non-boundary area using thetransferred filter information and the threshold values and thenperforms filtering on each of the areas.

For instance, in case of a boundary area, it is able to use a small-sizefilter to prevent a boundary area part from being excessivelysmoothened. On the contrary, in case of a non-boundary area, it is ableto use a larger-size filter to remove noise generated from aquantization process.

A process of applying a filter by partitioning a region of a frameaccording to a first embodiment of the present invention is explained.

First of all, one frame is divided by N*N size. IT is determined whetherto perform filtering on each N*N region. Based on this, it is able togenerate a filtering map indicating whether to perform filtering. If itis determined to perform the filtering, it is able to generate filtercoefficient suitable for each N*N region. The filter information and thefiltering map are transferred to a decoder. Subsequently, the decoderperforms filtering on a predicted frame using the filter information andthe filtering map.

FIG. 6 is a schematic block diagram of a video signal encoding apparatus(300) according to a second embodiment of the present invention.

Referring to FIG. 6, a transforming unit (310), a quantizing unit (315),a coding control unit (320), a inverse-quantizing unit (330), aninverse-transforming unit (335), a deblocking filtering unit (340), afiltering unit (345), a decoded picture storing unit (350), a motionestimating unit (355), an inter predicting unit (360), an intrapredicting unit (370) and an entropy coding unit (380). Thisconfiguration is identical to that shown in FIG. 1 except the filteringunit (345). The filtering unit (345) applies a filter to a picturedecoded through a deblocking filter to minimize a difference from anoriginal picture.

FIG. 7 is a schematic block diagram of a video signal decoding apparatus(400) according to a second embodiment of the present invention.

Referring to FIG. 7, a video signal decoding apparatus according to thepresent invention includes an entropy decoding unit (410), ainverse-quantizing unit (420), an inverse-transforming unit (425), adeblocking filtering unit (430), a filtering unit (435), a decodedpicture storing unit (440), an inter predicting unit (450) and an intrapredicting unit (460). This configuration is identical to that shown inFIG. 2 except the filtering unit (435). The filtering unit 435 applies afilter to a picture decoded through a deblocking filter to minimize adifference from an original picture.

FIG. 8 is a flowchart of a process for applying a filter to a currentframe through a deblocking filtering unit in an encoder according to asecond embodiment of the present invention.

First of all, a filtering unit receives a current frame reconstructedthrough a deblocking filtering unit [S400]. The filtering unit comparesthe current frame and an original frame to each other and is then ableto generate a filter minimizing a difference between the two frames[S405]. A method of generating the filter will be explained withreference to FIG. 10.

Yet, although accuracy for reconstruction of the current frame isimproved by applying the generated filter to the current framereconstructed through the deblocking filtering unit, it may even lowerthe accuracy [S410]. If the filter application is efficient, thegenerated filter coefficient will be transferred to a decoder [S415]. Ifthe filter application is insufficient, information indicating that thefilter will not be applied to a predicted frame is transferred using aflag [S420].

FIG. 9 is a flowchart of a process for applying a filter to a currentframe through a deblocking filtering unit in a decoder according to asecond embodiment of the present invention.

First of all, a decoder receives filter information on a current framefrom an encoder [S425] and then applies the filter information to areconstructed current frame through a deblocking filtering unit [S430].The current frame through the filtering unit is outputted or can bestored in a decoded picture storing unit to be used for another frameprediction [S435].

FIG. 10 is a schematic diagram for a method of generating a filteraccording to the present invention.

Referring to FIG. 10, w[n]′ indicates a predicted pixel value of acurrent picture and is a value inputted to a filter. And, x[n]′ is apredicted pixel value of a filtered current picture. In case that afilter of order N and with coefficients a_(i) is used, x[n]′ can berepresented as Formula 8.

$\begin{matrix}{{x\lbrack n\rbrack}^{\prime} = {\sum\limits_{i = 0}^{N}{a_{i}^{\prime}{w\left\lbrack {n - i} \right\rbrack}^{\prime}}}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Moreover, s[n]′ is a pixel value of an original picture. If a differencebetween x[n]′ and s[n]′ is set to e[n]′, it is able to obtain a_(i)′which minimizes the e[n]′ and a_(i)′ can be represented as Formula 9.

a _(i) ′=

E{e ² [n]′}  [Formula 9]

The E{e²[n]′} can be represented as Formula 10.

$\begin{matrix}\begin{matrix}{{E\left\{ {e^{2}\lbrack n\rbrack}^{\prime} \right\}} = {E\left\{ \left( {{x\lbrack n\rbrack}^{\prime} - {s\lbrack n\rbrack}^{\prime}} \right)^{2} \right\}}} \\{= {{E\left\{ {x^{2}\lbrack n\rbrack}^{\prime} \right\}} - {E\left\{ {s^{2}\lbrack n\rbrack}^{\prime} \right\}} - {2E\left\{ {{x\lbrack n\rbrack}^{\prime}{s\lbrack n\rbrack}^{\prime}} \right\}}}} \\{= {{E\left\{ \left( {\sum\limits_{i = 0}^{N}{a_{i}^{\prime}{w\left\lbrack {n - i} \right\rbrack}^{\prime}}} \right)^{2} \right\}} + {E\left\{ {s^{2}\lbrack n\rbrack}^{\prime} \right\}} -}} \\{{2E\left\{ {\sum\limits_{i = 0}^{N}{a_{i}^{\prime}{w\left\lbrack {n - i} \right\rbrack}^{\prime}{s\lbrack n\rbrack}^{\prime}}} \right\}}}\end{matrix} & \left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack\end{matrix}$

If it is differentiated to find the which minimizes the expressionabove, Formula 11 is obtained.

$\begin{matrix}{{\frac{\partial}{\partial a_{i}^{\prime}}\begin{matrix}{{E\left\{ {e^{2}\lbrack n\rbrack}^{\prime} \right\}} = {{2E\left\{ {\left( {\sum\limits_{j = 0}^{N}{a_{j}^{\prime}{w\left\lbrack {n - j} \right\rbrack}^{\prime}}} \right){w\left\lbrack {n - i} \right\rbrack}^{\prime}} \right\}} -}} \\{{2E\left\{ {{s\lbrack n\rbrack}^{\prime}{w\left\lbrack {n - i} \right\rbrack}^{\prime}} \right\}}} \\{{\left. {= {2{\sum\limits_{j = 0}^{N}{E\left\{ {w\left\lbrack {n - j} \right\rbrack}^{\prime} \right){w\left\lbrack {n - i} \right\rbrack}^{\prime}}}}} \right\} a_{j}^{\prime}} -} \\{= {{- 2}E\left\{ {{w\left\lbrack {n - i} \right\rbrack}^{\prime}{s\lbrack n\rbrack}^{\prime}} \right\}}}\end{matrix}}{{i = 0},\ldots \mspace{14mu},N}} & \left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack\end{matrix}$

If w[n]′ and s[n]′ are stationary, R_(w)[m]′ and R_(ws)[m]′ knownrespectively as the autocorrelation of w[n]′ and the cross-correlationbetween w[n]′ and s[n]′ are defined as Formula 12.

R _(w) [m]′=E{w[n]′w[n+m]′}

R _(ws) [m]′=E{w[n]′s[n+m]′}  [Formula 12]

The Formula 11 can be represented as Formula 13 by using the Formula 12.

$\begin{matrix}{{{\frac{\partial}{\partial a_{i}^{\prime}}E\left\{ {e^{2}\lbrack n\rbrack}^{\prime} \right\}} = {{2{\sum\limits_{j = 0}^{N}{{R_{w}\left\lbrack {j - i} \right\rbrack}^{\prime}a_{j}^{\prime}}}} - {2{R_{sw}\lbrack i\rbrack}^{\prime}}}}{{i = 0},\ldots \mspace{14mu},N}} & \left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack\end{matrix}$

The a_(i)′ is obtained by letting the derivative be equal to zero.

$\begin{matrix}{{\begin{bmatrix}{R_{w}\lbrack 0\rbrack}^{\prime} & {R_{w}\lbrack 1\rbrack}^{\prime} & \ldots & {R_{w}\lbrack N\rbrack}^{\prime} \\{R_{w}\lbrack 1\rbrack}^{\prime} & {R_{w}\lbrack 0\rbrack}^{\prime} & \ldots & {R_{w}\left\lbrack {N - 1} \right\rbrack}^{\prime} \\\vdots & \vdots & \vdots & \vdots \\\vdots & \vdots & \vdots & \vdots \\{R_{w}\lbrack N\rbrack}^{\prime} & {R_{w}\left\lbrack {N - 1} \right\rbrack}^{\prime} & \ldots & {R_{w}\lbrack 0\rbrack}^{\prime}\end{bmatrix}\begin{bmatrix}a_{0}^{\prime} \\a_{1}^{\prime} \\\vdots \\\vdots \\a_{N}^{\prime}\end{bmatrix}} = \begin{bmatrix}{R_{sw}\lbrack 0\rbrack}^{\prime} \\{R_{sw}\lbrack 1\rbrack}^{\prime} \\\vdots \\\vdots \\{R_{sw}\lbrack N\rbrack}^{\prime}\end{bmatrix}} & \left\lbrack {{Formula}\mspace{14mu} 14} \right\rbrack\end{matrix}$

The a_(i)′ can be obtained from the Formula 14.

A process of applying a filter by considering a type of macroblockaccording to a second embodiment of the present invention is explained.

First of all, an encoder is able to generate a macroblock map, on whicha type of a macroblock, i.e., an intra-macroblock or an inter-macroblockis marked. It is able to categorize a frame into a category including anintra-macroblock or an inter-macroblock only using the macroblock map.Filter information to be applied per category is generated. The filterinformation is then transferred to a decoder.

The decoder generates a macroblock map as well. A category is sorted pertype of macroblock using the generated macroblock map. Filtering isperformed by applying the filter information transferred from theencoder to each category.

A process of applying a filter by considering a quantization parameteraccording to a second embodiment of the present invention is explained.

First of all, a quantization parameter may differ per macroblock. If thequantization parameter is large, a range of quantized values is smalland a compression ratio is high. But, the quantized values have bigdifferences from an original signal. On the contrary, if a quantizationparameter is small, quantized values become proximate to an originalsignal but a compression ratio is lowered. Hence, the quantizationparameter affects an image quality of a reconstructed picture.

A category is sorted per quantization parameter of a macroblock. Afilter suitable for each macroblock can be generated with reference tothe category. The generated filter information is transferred to adecoder. It is then able to perform filtering per quantization parameterusing the generated filter information.

A process of applying a filter by considering a coded block pattern(CBP) according to a second embodiment of the present invention isexplained.

First of all, a coded block pattern (CBP) is a value indicating whetherdata exists within a macroblock. For instance, if a coded residual exitswithin a macroblock, reconstruction will be performed by adding theresidual to a predicted macroblock. If a coded residual fails to exitwithin a macroblock, reconstruction will be performed by a predictedmacroblock itself. Hence, a characteristic of an image may varyaccording to the CBP.

By considering the CBP, it is able to categorize a frame. It is able togenerate a filter suitable per category. The filter information istransferred to a decoder. It is able to perform filtering per CBP usingthe filter information.

A process of applying a filter by considering a boundary strengthaccording to a second embodiment of the present invention is explained.

First of all, a deblocking filter is provided to reduce a blockdistortion phenomenon and can be used by changing a strength of filter.But, a filter can not be used if efficiency of video signal processingis lowered due to the filter application. This depends on a boundarystrength and a variation of an image sample around a boundary. And, theboundary strength is determined according to a relation with a presenceor non-presence of an intra-coded macroblock, a motion vector value, areference block or the like. Hence, the boundary strength is related toa characteristic of image.

Based on a boundary strength, it is able to categorize a frame through adeblocking filter. It is able to generate a filter suitable for eachcategory. The filter information is transferred to a decoder. And, it isable to perform filtering per boundary strength using the filterinformation. Yet, in case that a filter is applied per category based onthe boundary strength, deblocking filtering is omitted.

A process of applying a filter by considering a boundary area accordingto a second embodiment of the present invention is explained.

First of all, it is able to apply a filter to each area by categorizinga frame into a boundary area and a non-boundary area. A filtering unitreceives a current frame reconstructed through a deblocking unit. Byperforming a boundary search on the current frame through the deblockingfilter based on threshold values for determining a presence ornon-presence of a boundary, it is able to obtain a boundary area and anon-boundary area. Filter information to be applied to the boundary areaor the non-boundary area is generated. The generated filter information,the threshold values and the like are transferred to a decoder. Thedecoder sorts a boundary area and a non-boundary area using thetransferred filter information and the threshold values and thenperforms filtering on each of the areas.

For instance, in case of a boundary area, it is able to use a small-sizefilter to prevent a boundary area part from being excessivelysmoothened. On the contrary, in case of a non-boundary area, it is ableto use a larger-size filter to remove noise generated from aquantization process.

FIG. 11 is a flowchart for a method of compensating for an illuminationintensity difference between an original frame and a reconstructed frameaccording to a third embodiment of the present invention.

For instance, in video signal processing such as interpolation forfinding an accurate motion vector, B-frame predicting process,deblocking process and the like, various rounding operations areperformed. Hence, a difference between an illumination intensity averagevalue of an original frame and an illumination intensity average valueof a reconstructed frame is generated.

First of all, it is able to obtain an illumination intensity averagevalue for a reconstructed frame and an illumination intensity averagevalue for an original frame [S600]. A value resulting from dividing theillumination intensity average value of the reconstructed frame by theillumination intensity average value of the original frame is obtained[S605]. The obtained value is transferred to a decoder [S610].

Subsequently, the decoder is able to compensate for an illuminationintensity of the reconstructed frame using the transferred value [S615].

Therefore, it is able to reduce errors caused by the various roundingoperations.

FIG. 12 is a diagram for a method of coding a filter coefficient usingflag information according to a fourth embodiment of the presentinvention.

First of all, an encoder generates a filter to be applied to (n−1)^(th)frame and a filter to be applied to n^(th) frame (10,15). Yet, in casethat the (n−1)^(th) frame is similar to the n^(th) frame, it is able toapply the filter for the (n−1)^(th) frame to the n^(th) frame. For this,it is able to use a flag instructing to apply a filter of the (n−1)^(th)frame to the n^(th) frame.

For instance, in case that the flag instructs to apply a filter of aprevious frame to a current frame, the filter information of the(n−1)^(th) frame (10) is used as a filter of the n^(th) frame. Thefilter information of the n^(th) frame (15) is not transferred to adecoder by being coded. Therefore, by reducing a bit size for the filterinformation transferred to the decoder, video signal processing can beefficiently performed. On the contrary, in case that the flag does notinstruct to apply a filter of a previous frame to a current frame, thefilter information of the n^(th) frame (15) is transferred to a decoderby being coded.

FIG. 13 is a diagram for a method of coding filter information using adifference filter according to a fourth embodiment of the presentinvention.

First of all, an encoder generates a filter to be applied to (n−1)^(th)frame and a filter to be applied to n^(th) frame (30,35). And, an n^(th)difference filter (40), which is a difference between the filter of the(n−1)^(th) frame and the filter of the n^(th) frame is obtained. Intransferring filter information of the n^(th) frame to a decoder, theencoder is able to reduce a bit size by transferring the n^(th)difference filter information (40) to the decoder only.

Subsequently, the decoder is able to obtain the filter of the n^(th)frame using the transferred nth difference filter information (40) andthe filter information of the (n−1)^(th) frame (30).

FIG. 14 is a diagram for a method of coding filter information using aprediction filter according to a fourth embodiment of the presentinvention.

First of all, after filter information of each frame for a wholesequence has been generated, a prediction filter can be regarded as anaverage value of the filter information. An encoder generates filterinformations of frames (45,46) and then obtains difference filterscorresponding to differences between the prediction filter and the framefilters (48,60), respectively. Subsequently, the encoder transfers thedifference filters and the prediction filter to a decoder. The decoderis able to obtain the filers of the frames using the difference filters(48,50) and the prediction filters (47,49), respectively. Therefore, afiler information size transferred to the decoder is reduced, wherebyvideo signal processing can be efficiently performed.

Moreover, the prediction filter is not limited by the filter informationaverage value of the respective frames for the whole sequence. And, itis able to use a filer of an (n−1)^(th) frame as a prediction filter foran n^(th) frame. Hence, it means that the prediction filter used for then^(th) frame (49) can be updated by the prediction filter of the(n−1)^(th) frame (47) and the (n−1)^(th) difference filter (48). Ifthere is a big difference between the prediction filter and the filterof the n^(th) frame, it may be inefficient to use the prediction filteras it is. Instead, it may be efficient to use a filer similar to thefilter of the n^(th) frame as the prediction filter.

INDUSTRIAL APPLICABILITY

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1-23. (canceled)
 24. A method of decoding a video signal with a videodecoding apparatus, comprising: receiving, with the video decodingapparatus, the video signal, the video signal including first flaginformation for a current picture, the first flag information indicatingwhether an adaptive filter is applied or not; reconstructing, with thevideo decoding apparatus, the current picture; performing, with thevideo decoding apparatus, a deblocking-filtering on the reconstructedcurrent picture; and performing, with the video decoding apparatus, anadaptive-filtering on the deblocking-filtered current picture based onthe first flag information.
 25. The method of claim 24, wherein theperforming the adaptive-filtering comprises obtaining, with the videodecoding apparatus, second flag information based on the first flaginformation, the second flag information indicating whether filtercoefficients of an N^(th) adaptive filter is derived from filtercoefficients of an (N−1)^(th) adaptive filter; and obtaining, with thevideo decoding apparatus, the filter coefficients of the N^(th) adaptivefilter based on the second flag information, wherein N is a naturalnumber and greater than
 1. 26. The method of claim 25, wherein theobtaining the filter coefficients of the N^(th) adaptive filtercomprises: extracting, with the decoding apparatus, difference filtercoefficients of the N^(th) adaptive filter from the video signal; andderiving the filter coefficients of the N^(th) adaptive filter using thedifference filter coefficients of the N^(th) adaptive filter andprediction filter coefficients when the second flag informationindicates that the filter coefficients of the N^(th) adaptive filter isderived from the filter coefficients of the (N−1)^(th) adaptive filter,the prediction filter coefficients being from the filter coefficients ofthe (N−1)^(th) adaptive filter.
 27. The method of claim 24, wherein theadaptive-filtering is performed by considering a quantization parameterof a macroblock.
 28. The method of claim 24, wherein theadaptive-filtering is performed by considering a coded block pattern(CBP) of a macroblock.
 29. The method of claim 24, wherein theadaptive-filtering is performed by considering a block boundary strengthbetween blocks and by omitting performing the deblocking-filtering onthe decoded picture.
 30. The method of claim 24, wherein performing theadaptive-filtering further comprises searching for a boundary areawithin a picture, wherein the adaptive-filtering includes discriminatingbetween the boundary area and a non-boundary area.
 31. The method ofclaim 24, further comprising: compensating, with the video decodingapparatus, for an illumination intensity difference between an originalpicture and the adaptive-filtered decoded picture.